Organic biomarkers characterisation in peat samples

N-alkanes, n–alkanoic acids are synthesized as part of the epicuticular leaf wax of plants. They can be used as paleoenvironmental proxies thanks to stability and weak solubility in water, especially for the long chain n-alkanes that are present only in leaves. The study of modern plants shows a clear predominance of chains with odd carbon number in n-alkanes and of even chains in n-alkanoic acids: this information could be used as indicator of the origin of molecules (natural vs petrogenic) and of bacterial degradation. Characteristic n-alkanes fall in the range C15-C31: the distribution pattern and dominant chain lengths of n-alkanes and n- alkanoic acids can be used in a multi-proxy analysis in order to reconstruct the composition of plant population and climate fluctuations [1]. Although the instrumental analysis of n-alkanes, normally performed by GC-FID, is widely employed, the characteristics of complex matrices such as peat require particular care in the extraction and purification procedures. In this work, GC-MS (Agilent 7890 – 5975c) methods for the detection of C10 to C36 n-alkanes and C11 to C24 n-alkanoic acids have been developed. The extraction was carried out by Pressurized Liquid Extraction PLE using a DCM:n-hexane mixture. Extracts were subsequently concentrated under a gentle stream of nitrogen and the clean- up was performed on silica gel SPE cartridges, collecting an apolar and a polar fraction separately, by eluting samples with a mixture of n-hexane:DCM followed by DCM:MeOH. Literature data often report palmitic and stearic acids as dominant species in samples, but rarely blank values are discussed [2]. In the present work, large amounts (ng to tens of ng) of C16 and C18 have been detected in laboratory blanks and mainly in SPE tubes, therefore requiring a strong conditioning with 40 mL of each solvent. The fractions were re-concentrated to about 100 μL and, before GC-MS analyses, the polar fraction was derivatized at 60°C. The method was finally tested on a small batch of samples from a peat bog located in the Dolomites.